1. Field of the Invention
The invention relates to a shift control apparatus and shift control method for a vehicular automatic transmission, which enables suppression of a drop in rotational speed of an input shaft which occurs during a clutch-to-clutch downshift executed while a vehicle is decelerating.
2. Description of the Related Art
A shift control apparatus for a vehicular automatic transmission is known which, when executing a clutch-to-clutch downshift, executes shift hydraulic pressure control so as to reduce an apply pressure of a hydraulic friction device to be released, which was applied in order to achieve a predetermined speed before the downshift, while increasing an apply pressure of a hydraulic friction device to be applied in order to achieve a predetermined speed after the downshift. According to JP(A) 11-287318, for example, during the clutch-to-clutch downshift, feedback control is performed on the apply pressure of the hydraulic friction device to be applied so that a transmitted torque capacity of the hydraulic friction device to be applied becomes constant, i.e., so that a rotational speed of an input shaft of the automatic transmission increases at a constant rate.
In the aforementioned shift control apparatus for a vehicular automatic transmission, the engine speed drops during the clutch-to-clutch downshift when the vehicle is decelerating, and then increases again when the hydraulic friction device to be applied is applied. This combination of a drop followed by an increase in engine speed results in shift shock or a delay in the shift time. Also, fuel efficiency may be reduced if the drop in engine speed is large enough to require that the fuel supply be restarted.